Gasoline containing alkyl dihydrogen phosphate as a corrosion inhibitor



2,996,367 Patented Aug. 15, 1961 2,996,367 GASOLINE CONTAINING ALKYL DIHYDROGEN PHOSPHATE AS A CORROSION INHIBITOR George W. Eckert, Wappingers Falls, and Howard V.

Hess, Glenham, N.Y., assignors to Texaco Inc., a corporation of Delaware N Drawing. Filed Nov. 12, 1958, Ser. No 773,185

1 Claim. (Cl. 44-69) This invention relates to a hydrocarbon fuel composition characterized by excellent anti-rust properties. More particularly, it involves the discovery that the corrosive and rusting properties of commercial gasolines are inhibited by the addition thereto of a small quantity of a particular class of organo phosphate esters.

The hydrocarbon fuels of this invention contain 8 to 50 lbs. per thousand barrels of alkyl dihydrogen phosphates of the general formula:

wherein R is an aliphatic hydrocarbon radical containing 4 to 18 carbon atoms. The presence of the prescribed amount of alkyl dihydrogen phosphate produces a fuel characterized by freedom from rust in severe corrosion tests.

Gasoline and jet fuels, which are often stored over water, tend to corrode, fuel systems and storage tanks wherein the fuel comes in contact with metal such as iron, copper, zinc and the like. The corrosion problem is particularly acute with leaded gasoline wherein the componnets of the tetraethyl lead fluid act as corrosion promoters. This invention provides corrosion inhibitors, namely, the alkyl dihydrogen phosphates, which inhibit the corrosive tendencies of leaded gasoline, jet fuels, and diesel fuels when added thereto in prescribed concentration. Alkyl dihydrogen phosphates are particularly useful in formulating non-corrosive high octane motor fuels disclosed in the commonly assigned copending application Serial No. 689,466, filed October 11, 1957, in the name of G. W. Eckert. The copending application discloses that the addition of a hydrocarbyl monocarboxylic acid in the concentration of atleast 0.1 volume percent to a high octane leaded motor fuel containing a substantial concentration of aromatic hydrocarbons, olefinic hydrocarbon or mixtures thereof causes a substantial improvement in the octane rating of the fuel. The lower hydrocarbon monocarboxylic acids, that is, those containing from about 2 to about 12 carbon atoms, aggravate the corrosive and rusting properties of the high octane fuel. The subject invention provides a solution to the corrosion problem resulting from the action of the lower hydrocarbon monocarboxylic acids as octane appreciators.

The alkyl di-acid phosphates employed as corrosion inhibitors in the fuel compositions of this invention have the general formula:

wherein R is an aliphatic hydrocarbon radical containing 4 to 18, and preferably 6 to 12 carbon atoms. Examples of effective alkyl dihydrogen phosphates are butyl dihydrogen phosphate, hexyl dihydrogen phosphate, octyl dihydrogen phosphate, dodecyl dihydrogen phosphate,

2 pentyl dihydrogen phosphate, heptyl dihydrogen phosphate and stearyl dihydrogen phosphate.

The specificity of the action of the prescribed C to C alkyl dihydrogen phosphates in preventing corrosion of fuels is one of the features of this invention. Apparently, alkyl dihydrogen phosphates of the prescribed formula have the proper balance of hydrophilic and lipophilic properties to act as both water and oil phase inhibitors. Alkyl dihydrogen phosphates wherein the alkyl radical contains less than 4 carbon atoms are too oil insoluble to function as corrosion inhibitors whereas alkyl dihydrogen phosphates wherein the alkyl radical contains more than about 18 carbon atoms possess too little water solubility to act as effective corrosion inhibitors. Alkyl dihydrogen phosphates containing 4 to 18 carbon atoms are significantly better than dialkyl hydrogen phosphates, trialkyl phosphates or alkyl pyrophosphates as corrosion inhibitors for gasoline and other distillate fuels.

An additional advantage accruing from the use of C to C alkyl dihydrogen phosphates as corrosion inhibitors in gasoline is the fact that the resulting gasoline, in addition to having improved corrosion resistant properties, is characterized by improved surface ignition properties. The C plus alkyl dihydrogen phosphates when employed in corrosion inhibiting amounts, supply 0.015 to 0.2 mol of phosphorus per mol of lead in the engine and reduce the tendency of the fuel to surface ignition during engine operation.

The amount of alkyl dihydrogen phosphate required to effectively inhibit the corrosive tendencies of gasoline fuels is a minimum of about 8 lbs. of C to C alkyl dihydrogen phosphate per 1000 bbls. of fuel. The usual concentration of'the alkyl dihydrogen phosphate is between 16 and 40 lbs. per 1000 bbls. The practical upper limit of the alkyl dihydrogen phosphate concentration is about 50 lbs. per 1000* bbls.

The superiority of alkyl dihydrogen phosphates to V closely-related alkyl phosphates and phosphites was demonstrated by the so-called Quickie Corrosion Test which -is performed as follows:

A /2" x 5" 16-gauge cold rolled steel strip which has been highly polished with an emery cloth, washed with acetone and dried in air, is immersed in cc. of the test fuel and 20 cc. of water in a 4-ounce tall-form bottle. The bottle is then shaken for 15 seconds in a horizontal position after which it is turned upright on a fiat surface. After standing for 24 hours, corrosion readings on the portion of the strip immersed in the fuel phase are estimated by visual inspection and are expressed in percent rust on the strip.

In Table I there is shown the effectiveness of various alkyl phosphates in inhibiting the corrosion of a leaded premium and a leaded regular grade gasoline. The various fuels employed in Table I are identified as follows:

Base Fuel A was a premium grade gasoline having a Research Octane No. (RON) of about 99.0 and com- .prised approximately 39 percent saturates, 31 percent 3 base lubricating oil oxidate having a Neut. No. between 55 and 80, a Sap. No. between 100 and 200 and an unsaponifiable content less than about 5 5 percent by weight. A detailed description of this refined oil oxidate corro- 4 complete corrosion protection with a leaded regular grade fuel such as Base Fuel C, which did not contain a corrosion inhibitor.

The results obtained with the lubricating oil oxidate sion inhibitor is found in the commonly assigned co- 5 corrosion inhibitor containing premium and regular fuels, pending application Serial No. 710,856, filed January 24, Base Fuels B and D resp y, also (1611101183316 the 195s, in the names of G. B. Kirkwood and J. H. Greene. outstanding superiority of alkyl dihydrogen phosphates Base F l C was a regular grade gasoline having an to closely-related phosphates as corrosion inhibitors. 16 RON of about 92 and comprised approximately 59 per- 1 P Q Q P methyl Phosphate was compleiely cent saturates, 20 percent olefins and 21 percent aromatl meffecllve mhlbltmg regular fuel B Fuel agamst ics by FIA analysis. Base Fuel C also contained 3 cc. Forroslon, Whereas of octyl dlhydrfgen of TEL fluid per gallon and had an IBP of 92 F. and an m run 4 provlded complete pmtectlon slmilafly end point of F. 8 lbs. per 1000 bbls. of octyl drhydrogen phosphate in run Base Fuel D was Base Fuel C plus 18 lbs. per 1000 No. 3 provided complete rust protectlon 1n Base Fuel B bbls. of the refined paraffin lubricating oil oxidate cor- 15 Whereas-a mlxture of octyl dlhydrogen phqsphate and rosion inhibitor employed with Base Fuel diocty-l hydrogen phosphate having an effective concen- T he data in Table I demonstrate conclusively the supeanon of the octyl; dlhydfogep per 1000 bbls" riority of alkyl dihydrogen phosphates as corrosion inmefiecuve m mhlbmng Base Fuel B hibitors over closely-related phosphates such as dialkyl agamst corrosion hydrogen phosphates and trialkyl phosphates. In pre- In T?b1e H there Is demortstrated efiecuveness. mium fuel which did not contain an added corrosion alkyl dlilydrogen phosghaiws m preventmg the inhibitor, namely Base Fuel A, complete protection ofpremmm. filels contalmng hydrocaflwl monocarboxyhp against corrosion was provided by 16 lbs. per 1000 bbls. aclds contalmpg L30 .carbon atoms. as .octane f of octyl dihydrogen phosphate A 5040. mixture of ators. As disclosed n the afore-1dent1fied copendtng octyl dihydrogen phosphate and dialkyl hydrogen p G. Echert application Serial No. 689,466, monocarphates, to wit, run No. 11, wherein the effective concenboxyhc aclds coPcent'rafions of to Volume P tl-ation f the alkyl dihydrogen phosphate was 1 lbs. per cent substantially mcrease the octane rating of leaded 1000 bbls was unable to hi i completely corrosion gasoline containing a substantial concentration of aroi B F l A i di i h h dioctyl hydrogen h matics and olefins. A disadvantage of the use of lower phate component not only was not contributing to the molecular Weight C to C monocarboxylic acids as occorrosion protection but was actually having an adverse effect thereon.

tane appreciators is their tendency to increase the corrosive properties of the leaded fuel. A particularly im- 1 Rust percent is percent of metal surface covered by rust.

The data in the above table on Base Fuels A and C also demonstrate the necessity of employing the prescribed 8-50 lbs. of alkyl dihydrogen phosphate per 1000 bbls. in order to obtain corrosion protection. The lower limit of 8 lbs. per 1000 bbls. is set by the fact that 8 lbs. 70

TABLE I Effectiveness of various alkyl phosphates in inhibiting the corrosive properties of leaded fuels 1 Cone,

Run No. Inhibitor Ho 200 Base Fuel A Base Fuel B Base Fuel 0 Base Fuel D 1- Nrme Rust (75%). Rust (Ml-40%).. Rust (75%) Rust (50-60%). 2 Oetyl dihydrogen phosphate 4 Tra)c7e)Rust (6 Rust a a dn 8 N Bust dn Tr% $)Ru5t-, (5-

1 0 4 do 16 No Rust do Trace Rust No Rust.

(IO-15%). 5 24 Trace Rust Do.

6 32 No Rust No Rust Do. 7 do 40 do 8 5050 Mixture of Methyl Dihy- 16 Rust drogen Phosphate and D1- methyl Hydrogen Phosphate. 9 50-50 Mixture of Butyl Dihy- 16 Bust (GO-%).- Rust (30-40%). drogen Phosphate and Dibutyl Hydrogen Phosphate. 10 50-50 Mixture of Octyl Dihydro- 16 Rust (IO-20%).- Rust (IO-30%).- Rustgen Phosphate and Dioctyl Hydrogen Phosphate. 11 "do 32 Rust (lo-20%)-- 12 50-50 Mixture of Iso-arnyl Dihy- 16 Bust (20-30%).

drogen Phosphate and Di-isoamyl Hydrogen Phosphate. 13 Triethyl Phosphate 16 Rust (5 0%)- portant feature of the subject invention is that the alkyl dihydrogen phosphates are effective in controlling the corrosion of monocarboxylic acid-containing gasolines in concentrations of 8-50 lbs. per 1000 bbls.

The fuel employed in Table II is the leaded corrosion inhibited premium gasoline, Base Fuel B, employed in Table I having an RON of 99. The addition of 0.5 volume percent Z-ethylhexanoic acid to Base Fuel B raised the RON from 99.0 to 100.0 while the addition of 0.5 weight percent benzoic acid raised the octane rating of the fuel from 99.0 to 100.8.

TABLE II Efiectiveness of alkyl dihydrogenphosphate in inhibiting corrosion of monocarboxylic acid-containing premium gasoline Base Fuel B+ Run Inhibitor Cone, lbs./ 0.5 v. percent Base Fuel B+0.5 w. percent Nos. 1,000 bbls. 2-ethylhex- Benzoic anoic None .s Rust Rust (20-50%) Octyl dihydrogen phosphate- 16 Trace Rust.-. N o Rust.

d 32 N o Rust Monostearyl dihydrogen phosphate 50-50 mixture of butyl dihydrogen phosphate and dibutyl hydrogen phosphate.

50-50 mixture of octyl dihydrogen phosphate and dioctyl hydrogen phosphate.

Triethyl phosphate 50-50 mixture of amyl dihydrogen phosphate and diamyl hydrogen phosphate.

50-50 mixture of lauryl dihydrogen phosphate and dilauryl hydrogen phosphate.

Di-Z-ethylhexyl phosphite Dioctyl acid pyrophosphate N Rust in gasoline layer. Rust in H2O layer. Rust (20-40%).

Rust (20-50%). Rust (20-40%).

Rust (-407 The data in Table II demonstrate the eifectiveness of alkyl dihydrogen phosphates in eliminating the corrosive action of monocarboxylic acid octane appreciators in leaded fuels. In run No. 3, 32 lbs. per 1000 bbls. of octyl dihydrogen phosphate completely inhibited the corrosive properties of a leaded premium fuel containing 0.5 volume percent Z-ethylhexanoic acid and in run No. 2,

16 lbs. per 1000 bbls. of the same compound inhibited the corrosive properties of a leaded premium fuel containing 0.5 weight percent benzoic acid. In run No. 4, monostearyl dihydrogen phosphate in a concentration of 16 lbs. per 1000 bbls. was efiective in eliminating rust from the gasoline layer of a benzoic acid-containing leaded premium fuel but permitted a minor amount of rusting in the water layer. As shown in run Nos. 5, 6, 8, and 9, -50 mixtures of alkyl dihydrogen phosphates and dialkyl hydrogen phosphates were inefiective in preventing corrosion in a benzoic acid-containing leaded premium fuel. Similarly, triethyl phosphate, di-Z-ethylhexyl phosphate and di-octyl acid pyrophosphate, run Nos. 7, 10 and 11, respectively, were ineifective in preventing corrosion in a benzoic acid-containing leaded premium fuel. 45

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claim.

We claim:

A leaded gasoline containing a refined paraffin base lubricating oil oxidate having a Neut. No. between and 80, a Sap. No. between and 200 and an unsaponifiable content less than about 55% by weight in a concentration of approximately 18 pounds per thousand barrels and octyl dihydrogen phosphate in a concentration of 8 to 50 pounds per thousand barrels.

References Cited in the file of this patent UNITED STATES PATENTS 2,080,299 Benning et a1 May 11, 1937 2,167,867 Benning Aug. 1, 1939 2,340,331 Knutson et a1 Feb. 1, 1944 2,784,208 Ries Mar. 5, 1957 2,851,343 Cantrell et al. Sept. 9, 1958 FOREIGN PATENTS 600,191 Great Britain Apr. 2, 1948 640,311 France Mar. 26, 1928 

